Communication system, transmission terminal and reception terminal

ABSTRACT

A receiving terminal  2  calculates jitter moving average from the transmission and the reception time of each packet and sends the moving average to a transmitting terminal  1 , and based on the jitter moving average, the transmitting terminal predicts an available bandwidth in a radio path.

TECHNICAL FIELD

[0001] The present invention relates to a communication system,transmitting terminal and a receiving terminal which implement anefficient packet delivery in a communication environment containing aradio path.

BACKGROUND ART

[0002] The deterioration of the operating condition for a packetcommunication in a wire environment is attributable to the congestionresulting from concentration of many packets in a narrow-bandwidth pathwhich forms a communication bottleneck; usually, reduction in thebandwidth is not caused by worsening of the connecting condition of thepath itself. That is, the upper limit of the overall bandwidth availableon the path is fixed. Accordingly, the quality of communication betweentransmitting and receiving terminals could be improved by detecting thecongestion on the path and performing delivery control in accordancewith the congestion.

[0003] On the other hand, the deterioration of the operating conditionfor a packet communication in the radio environment is affected not onlyby the packet congestion but also by aggravation of the communicationcircumstance due to a change in the connecting condition of the radiopath.

[0004] Generally, the bit error rate of the communication in the radioenvironment is higher than that in the wire environment, and in thepacket communication a packet containing a bit error is often regardedas invalid (i.e., a packet loss) in its entirety. For that, in manyinstances, an error correcting mechanism deals with the packet loss byresending the packet being lost or sending a redundant packet from thetransmitting terminal in a data link layer or lower than that layer.

[0005] With the presence of the error correcting mechanism, however, itappears from the user side that the actual packet loss probability isnot so high as the bit error rate. But, when the delay time byprocessing in the error correcting mechanism increases, it is observedas if a decrease in the throughput or in the available bandwidth iscaused. As a result, the available bandwidth itself also undergoesvariations. That is, the upper limit of the overall bandwidth availableon the path also varies.

[0006] If the packet delivery is continued in spite of such variations,the situation will also arise where the packet transfer in excess of theavailable bandwidth continues, which causes a further increase in thedelay or packet loss. This leads to quality deterioration of continuousmedia information or the like in particular which needs to be deliveredon a real-time basis.

[0007] In the radio environment the communicating conditions becomedeteriorated typically when a mobile terminal makes handover. As adelivery control scheme adaptable to a change in the conditions ofcommunication by handover, there is, for example, “A Traffic ControlScheme of Live Video and Audio for PHS with a 64 kbps Bearer Service ofBest Effort Type,” Technical Report of IEICE, CQ99-81 (2000-02). Thisscheme is to measure RTT (Round-Trip-Time) between transmitting andreceiving terminals and control the packet delivery according to themeasured RTT value.

[0008] In addition, it is also considered to utilize intact a schemewhich performs communication control according to the congestion in thewire environment. In particular, many systems using such a schememonitor the congestion by detecting the packet loss. But the schemebased on the packet loss detection is a postprocessing type.

[0009] Since the conventional communication system has such aconfiguration as described above, if the communicating conditions arebadly deteriorated as in the case of handover, it is possible to copewith such a situation in the postprocessing manner, but since thebandwidth available on the radio path is undetectable, it is impossibleto perform appropriate packet delivery control in accordance with thecommunication environment.

[0010] The present invention is intended to solve such a problem asmentioned above and has for its object to provide a communication systemand a transmitting terminal which permit detection of an availablebandwidth in the radio path and hence ensure an appropriate packetdelivery.

[0011] Furthermore, the present invention has for its object to providea receiving terminal which is capable of offering information necessaryfor a transmitting terminal to detect an available bandwidth in theradio path.

DISCLOSURE OF THE INVENTION

[0012] A communication system according to an aspect of the presentinvention has a configuration in which the receiving terminal calculatesa jitter moving average from the transmitting and the receiving time ofeach packet received by the receiving terminal and sends the calculatedjitter moving average to the transmitting terminal and, based on thejitter moving average, the transmitting terminal predicts an availablebandwidth on the radio path based.

[0013] With this configuration, it is possible to provide an appropriatepacket delivery in accordance with the radio environment.

[0014] A communication system according to another aspect of the presentinvention has a configuration in which the receiving terminal sends tothe transmitting terminal a jitter moving average calculated taking onlypositive-valued jitter into account and a jitter moving averagecalculated taking into account negative-valued jitter as well as thepositive-valued jitter, and the transmitting terminal compares the bothmoving averages and predicts an available bandwidth taking the result ofcomparison into account.

[0015] With this configuration, it is possible to make an accurateprediction of the available bandwidth in the radio path.

[0016] A communication system according to another aspect of the presentinvention has a configuration in which when the jitter moving averagecalculated taking account into account not only positive- but alsonegative-valued jitter is larger than the jitter moving averagecalculated taking into account only the positive-valued jitter, theavailable bandwidth is predicted based on the jitter moving averagecalculated taking into account only the positive-valued jitter.

[0017] With this configuration, it is possible to avoid the possibilityof the available bandwidth being predicted narrower than in the actualcondition of communication.

[0018] A communication system according to another aspect of the presentinvention has a configuration In which when the jitter moving averagecalculated taking account into account not only positive- but alsonegative-valued jitter is smaller than the jitter moving average takinginto account only the positive-valued jitter, the available bandwidth ispredicted based on the jitter moving average of jitter calculated takingaccount into account not only positive- but also negative-valued jitter,the available bandwidth is predicted based on the jitter moving averagecalculated taking into account only the positive-valued jitter, and anaverage of the results of both predictions is used as a final result ofprediction.

[0019] With this configuration, it is possible to decrease the bandwidthto a desired appropriate value even under poor conditions ofcommunication.

[0020] A communication system according to another aspect of the presentinvention has a configuration in which the difference between the jittermoving average calculated taking only positive-valued jitter intoaccount and the jitter moving average calculated taking into account notonly positive- but also negative-valued jitter and the result of theprevious prediction is updated in accordance with the ratio of thedifference to a predetermined threshold value.

[0021] With this configuration, it is possible to make an accurateprediction of the available bandwidth in the radio path.

[0022] A communication system according to another aspect of the presentinvention is configured to control the amount of packets to be sent inaccordance with the available bandwidth.

[0023] With this configuration, it is possible to send an appropriateamount of packets.

[0024] A communication system according to another aspect of the presentinvention is configured to control the packet send interval inaccordance with the available bandwidth.

[0025] With this configuration, it is possible to send packets atappropriate intervals.

[0026] A communication system according to another aspect of the presentinvention is configured to designate a packet error correcting scheme inaccordance with the available bandwidth.

[0027] With this configuration, it is possible to use an appropriatepacket error correcting scheme.

[0028] A communication system according to another aspect of the presentinvention has a configuration in which the transmitting terminal isconnected to a wire path and the receiving terminal is connected to aradio path.

[0029] With this configuration, it is possible to apply the system to acommunication system in which the receiving terminal is connected to theradio path.

[0030] A communication system according to another aspect of the presentinvention has a configuration in which the transmitting terminal isconnected to a radio path and the receiving terminal is connected to awire path.

[0031] With this configuration, it is possible to apply the system to acommunication system in which the transmitting terminal is connected tothe radio path.

[0032] A communication system according to another aspect of the presentinvention has a configuration in which transmitting and receivingterminal are both connected to a radio path.

[0033] With this configuration, it is possible to apply the system to acommunication system in which the transmitting and receiving terminalsare both connected to a radio path.

[0034] A communication system according to another aspect of the presentinvention has a configuration in which transmitting and receivingterminals are both connected to a wire path and a mobile terminal isprovided in the communication environment to relay packets from thetransmitting terminal to the receiving terminal.

[0035] With this configuration, it is possible to apply the system to acommunication system in which the mobile terminal is provided on thecommunication path to relay packets.

[0036] A communication system according to another aspect of the presentinvention has a configuration in which the receiving terminal calculatesa moving average of a reception delay time from each packet receptiontime and sends the calculated moving average to the transmittingterminal and, based on the moving average of the reception delay time,the transmitting terminal predicts the available bandwidth in the radiopath.

[0037] With this configuration, it is possible to provide an appropriatepacket delivery in accordance with the radio environment.

[0038] A transmitting terminal according to another aspect of thepresent invention is adapted to predict the available bandwidth on aradio path based on the jitter moving-average received from thereceiving terminal.

[0039] This provides an appropriate packet delivery in accordance withthe radio environment.

[0040] A receiving terminal according to still another aspect of thepresent invention is adapted to calculate the jitter moving average fromthe time of transmission of each packet from the transmitting terminaland the time of reception of the packet and send the calculated movingaverage to the transmitting terminal.

[0041] This makes it possible to provide information necessary for thetransmitting terminal to detect the available bandwidth on the radiopath.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a block diagram illustrating a communication systemaccording to a first embodiment of the present invention.

[0043]FIG. 2 is an explanatory diagram showing variations in a movingaverage of jitter.

[0044]FIG. 3 is a block diagram illustrating a communication systemaccording to a fourth embodiment of the present invention.

[0045]FIG. 4 is a block diagram illustrating a communication systemaccording to a fourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0046] To facilitate a better understanding of the present invention, adetailed description will hereinafter be given, with reference to theaccompanying drawings, of the best mode for carrying the invention.

First Embodiment

[0047]FIG. 1 is a block diagram illustrating a communication systemaccording to a first embodiment of the present invention. In FIG. 1,reference numeral 1 denotes a transmitting terminal connected to a wirepath to send packets, 2 denotes a receiving terminal connected via aradio path to a radio base station 3 to receive packets from thetransmitting terminal 1, and 3 the radio base station.

[0048] Reference numeral 11 denotes a radio interface control part; 12denotes a packet receiving part for receiving packets sent from thetransmitting terminal 1; 13 denotes a moving average calculating partfor calculating a moving average of jitter from the time of transmissionof each packet and the time of reception of the packet received by thepacket receiving part 12; and 14 denotes a reception state transmittingpart which sends the moving average of jitter calculated by the movingaverage calculating part 13, as a report indicating the state ofreception, to the transmitting terminal 1.

[0049] Reference numeral 21 denotes a transmission line interfacecontrol part; 22 denotes a reception state receiving part for receivingthe report sent from the receiving terminal 2; 23 denotes a path stateevaluating part which detects the moving average of jitter from thereport received by the reception state receiving part 22 and, based onthe moving average of jitter, predicts an available bandwidth in theradio path; 24 denotes a delivery control part for controlling theamount of packets to be sent and their sending interval in accordancewith the available bandwidth predicted by the path state evaluating part23; and 25 a packet transmitting part for sending packets to thereceiving terminal 2 under the control of the delivery control part 24.

[0050] Next, the operation of this embodiment will be described below.

[0051] In the first place, when packets are sent from the packettransmitting part 25 of the transmitting terminal 1, the packetreceiving part 12 of the receiving terminal 2 receives the packets.

[0052] When the packet receiving part 12 starts receiving the packets,the moving average calculating part 13 of the receiving terminal 2calculates the moving average of jitter from the time of transmission ofeach packet and the time of packet reception. Incidentally, let it beassumed that the information indicating the time of packet transmissionis contained in each packet being sent.

[0053] That is, as shown below, packet transmission and reception timeintervals are detected and the transmission time interval is subtractedfrom the reception time interval to obtain jitter D₁.

D _(i)=(R _(i) −R _(i−1))−(S _(i) −S _(i−1))  (1)

[0054] where: R₁ is an i-th packet receiving time;

[0055] R_(i−1) is an (i−1)th packet receiving time;

[0056] S₁ is an i-th packet transmitting time;

[0057] S_(i−1) is an (i−1)th packet transmitting time.

[0058] Then, after calculating the jitter D_(i) as described above, themoving average calculating part 13 of the receiving terminal 2substitutes the jitter D_(i) into the following equation defined in RTP(Real-time Transport Protocol, RFC1889) standardized by IETF to therebycalculate jitter moving average J_(i) concerning the i-th packet.

J _(i) =J _(i−1)+(|D _(i) |−J _(i−1))/16  (2)

[0059] Here, the value of jitter, even under a good communicationcondition in the radio environment, may sometimes become a largenegative value when the error correcting mechanism performs bit errorcorrecting if a bit error arises. This is a phenomenon that occursbecause the delay caused by the error correcting mechanism is eliminatedin the data link layer to provide matching of the overall throughput.Since Equation (2) performs the calculation by use of an absolute valueof the jitter D_(i), however, even if the communication condition isgood, the negative-valued jitter of a large absolute value is judgedmerely as indicating that the radio path is in a bad condition. Thisconstitutes an obstacle to an efficient use of the bandwidth.

[0060] In contrast thereto, when the communication condition in theradio environment becomes worse and the negative-valued jitter of alarge absolute value becomes negative-valued jitter of a small absolutevalue as the result of jitter having increased, the moving averagecalculated therefrom becomes small and the bad communication conditionmay not be properly judged in some cases.

[0061] To avoid this, when the moving average calculating part 13 of thereceiving terminal 2 calculates the jitter moving average J_(i) by useof Equation (2), it calculates the jitter moving average taking intoaccount not only negative- but also positive-valued jitter (which movingaverage will hereinafter be denoted by J_(i)*) and, at the same time,calculates a jitter moving average taking into account onlypositive-valued jitter (which moving average will hereinafter be denotedby J_(i) ⁺). (Assume that when jitter becomes negative-valued, thejitter moving average associated with the immediately preceding packetis used.)

[0062] When the moving average calculating part 13 has calculated thetwo kinds of moving averages J_(i)* and J_(i) ⁺ as mentioned above, thereception state transmitting part 12 of the receiving terminal 2 sendsthe two kinds of jitter moving averages J_(i)* and J_(i) ⁺, as a reportindicating the reception state, to the transmitting terminal 1.

[0063] The reception state receiving part 22 of the transmittingterminal 2 receives the report sent from the reception statetransmitting part 14 of the receiving terminal 2.

[0064] When the report is received by the reception state receiving part22, the path state evaluating part 23 of the transmitting terminal 1detects the jitter moving averages J_(i)* and J_(i) ⁺ from the reportand, based on these jitter moving averages J_(i)* and J_(i) ⁺, predictsan available bandwidth on the radio path.

[0065] More specifically, the available bandwidth on the radio path ispredicted as described below.

[0066] In the first place, the path state evaluating part 23 comparesthe jitter moving averages J_(i)* and J_(i) ⁺. At this time, there arecases where J_(i)*>J_(i) ⁺ as indicated in a time period A in FIG. 2 andwhere J_(i)*<J_(i) ⁺ as indicated in a time period B.

[0067] In the time period A, it is considered that the bit errorcorrecting processing by the error correcting mechanism on the radiopath brings forward the case where jitter takes many negative values oflarge absolute values. Hence, it is preferable to predict the availablebandwidth based on the moving average J_(i) ⁺ rather than to predict theavailable bandwidth based on the moving average J_(i)*. That is, thebandwidth is calculated substituting the moving average J_(i) ⁺ for avariable x of a function R(x) for calculating the available bandwidth.Incidentally, no particular limitation is imposed on the function R(x),but the function R( ) disclosed in Pat. Appln. Laid-Open Gazette No.2001-23080, for instance, is used.

[0068] As a result, it is possible to avoid the possibility of theavailable bandwidth being evaluated to be narrower than in the actualcommunication condition.

[0069] On the other hand, in the time period B it is considered thatjitter takes many negative values small in absolute value; hence, it ispreferable to evaluate the moving average J_(i) ⁺ as well as J_(i)*. Tothis end, the bandwidth is calculated substituting the moving averageJ_(i)* for the variable x of the function R(x) and, at the same time,the bandwidth is calculated substituting the moving average J_(i) ⁺ forthe variable x of the function R(x). Then, as shown below, the bandwidthR(J_(i)*) and the bandwidth R(J_(i) ⁺) is averaged, and the averagevalue R′ is determined as a final available bandwidth.

R′=[R(J _(i)*)+R(J _(i) ⁺)]/2  (3)

[0070] As a result, even if the communication condition is poor, when adesired bandwidth does not become narrow, it can be reduced to anappropriate value.

[0071] When the path state evaluating part 23 predicts the availablebandwidth, the delivery control part 24 of the transmitting terminal 1controls the amount and send interval of packets to be sent from thepacket transmitting part 25 in accordance with the predicted availablebandwidth. For example, if the available bandwidth is wide, the amountof packets to be sent is increased and the send interval is shortened,whereas when the available bandwidth is narrow, the amount of packets tobe sent is decreased and the send interval is lengthened.

[0072] The packet transmitting part 25 of the transmitting terminal 25sends packets to the receiving terminal 2 under the control of thedelivery control part 24.

[0073] As is evident from the above, according to the first embodiment,the receiving terminal 2 calculates the moving average of jitter fromthe transmission and reception times of each received packet and sendsthe calculated jitter moving average to the transmitting terminal 1, andthe transmitting terminal 1 predicts the available bandwidth on theradio path based on the received jitter moving average; hence, it ispossible to make an appropriate delivery of packets in accordance withthe radio environment.

Second Embodiment

[0074] While the first embodiment has been described to predict theavailable bandwidth on the radio path without specifying any particularradio communication scheme, it is also considered preferable to changethe available bandwidth according to the radio communication schemeused.

[0075] Then, a second embodiment will be described to predict theavailable bandwidth taking into account the radio communication schemeused.

[0076] In the second embodiment the transmitting terminal 1 calculates adifference between a jitter moving average calculated taking intoaccount positive-valued jitter alone and a jitter moving averagecalculated taking into account not only the positive- but alsonegative-valued jitter, and updates the previous predicted value inaccordance with the ratio of the difference to a predetermined thresholdvalue.

[0077] More specifically, in the first place, the path state evaluatingpart 23 of the transmitting terminal 1 calculates fluctuations Δ in theavailable bandwidth by substituting into the following Equation (4) themoving averages J_(i)* and J_(i) ⁺ calculated by the receiving terminal2. Incidentally, β in Equation (4) is a threshold value preset inaccordance with the radio communication scheme used.

In the case where |J _(i) *−J _(i) ⁺|<β:

Δ=|J _(i) *−J _(i) ⁺|/β

In the case where |J _(i) *−J _(i) ⁺|≧β:

Δ=1  (4)

[0078] And, the path state evaluating part 23 of the transmittingterminal 1 substitutes the fluctuations Δ in the available bandwidthinto the following Equation (5) to thereby predict the availablebandwidth on the radio path. Incidentally, W in Equation (5) is theprevious predicted value and W′ is the newly predicted availablebandwidth. Further, k is a positive constant preset in accordance withthe radio communication scheme used.

W′=W(1−Δ/k)  (5)

Third Embodiment

[0079] In the first and second embodiments described above, the deliverycontrol part 24 of the transmitting terminal 1 controls the amount andsend interval of the packets to be sent from the packet transmittingpart 25 based on the available bandwidth predicted by the path stateevaluating part 23, but provision may also be made for the transmittingterminal 1 to indicate a packet error correcting scheme to the receivingterminal 2 in accordance with the available bandwidth.

[0080] That is, when the communication condition in the radioenvironment becomes worse, the error correcting mechanism in the datalink layer or the lower layer performs the error correcting processing,resulting in an increase in the number of packets waiting for deliveryin a base station or halfway (at a router or the like) on thecommunication path; too large a number of packets waiting for deliverycauses packet losses in the base station and halfway on thecommunication path. This calls for further error correcting processingfor the packets lost.

[0081] There are some methods of correcting packets thus lost. It ispossible to use, for example, a packet resending method that indicatesthe loss of packet to the transmitting terminal 1 and resends the packetto the receiving terminal 2, or a method in which the transmittingterminal 1 sends a packet together with redundant information on thepacket so that when the packet is lost, the receiving terminal 2reconfigures the packet based on the redundant information.

[0082] The third embodiment gives attention to the latter method.

[0083] The latter method requires redundant information about the packetthat is sent from the transmitting terminal 1, and if the number ofpieces of such redundant information is increased when the communicationcondition becomes worse, the communication condition is furtherdeteriorated. Accordingly, it is effective means to switch the packetloss correcting method to a method which permits correction of morepackets even with the same amount of redundant information.Incidentally, in the case of such a correction method, more pieces ofredundant information are not required but the computational complexityincreases.

[0084] The third embodiment deals with the packet loss by switching theerror correcting method to one that enables more errors to be correctedon a step-by-step basis in accordance with the rate of an increase inthe jitter moving average being reported. What is meant by “enables moreerrors to be corrected” is that more packets can be corrected within acertain unit time.

[0085] More specifically, this embodiment calculates the availablebandwidth in the same manner as in the first and second embodimentsdescribed above, and sets a threshold value for the bandwidth and, whenthe bandwidth exceeds the threshold value, applies a more effectiveerror correcting method.

[0086] When the communication condition in the radio environmentrecovers, the error correcting method is switched back to the initialone with a view to suppressing the delay and computational load causedby the error correction.

Fourth Embodiment

[0087] While Embodiments 1 to 3 have been described as being applied tothe system in which the transmitting terminal 1 is connected to a wirepath and the receiving terminal 2 is connected to a radio path, theinvention may also be applied to a system in which the transmittingterminal 1 is connected to the radio path and the receiving terminal 2is connected to the wire path as shown in FIG. 3. In FIG. 3, referencenumeral 15 denotes a transmission line interface control part and 26denotes a radio interface control part.

[0088] Further, the invention may also be applied to a system in whichthe transmitting and receiving terminals 1 and 2 are both connected tothe radio path as depicted in FIG. 4.

[0089] Moreover, the invention may also be applied to a system in whichthe transmitting and receiving terminals are both connected to the wirepath and a mobile terminal is present in the communication environmentfor relaying packets sent from the transmitting terminal 1 to thereceiving terminal 2.

Fifth Embodiment

[0090] While the first to fourth embodiments have been described asbeing applied to the system in which the moving average calculating part13 of the receiving terminal 2 calculates the jitter moving average andthe path state evaluating part 23 of the transmitting terminal 1predicts the available bandwidth based on the jitter moving average, theinvention is not limited specifically thereto but may also be applied toa system in which, for example, the moving average calculating part 13of the receiving terminal 2 calculates a moving average of a receptiondelay time, R_(i)−R_(i-1), from receiving times R_(i) and R_(i−1) ofreceived packets and sends the calculated moving average to thetransmitting terminal 1 and, based on the moving average of thereception delay time, the transmitting terminal 1 predicts the availablebandwidth on the radio path. This scheme produces the same effect as thecase with the first to fourth embodiments described above.

INDUSTRIAL APPLICABILITY

[0091] As described above, the communication systems according to thepresent invention are suitable for implementation of an efficient packetdelivery, taking into account the communication condition on thecommunication path in the case where a radio path is contained in thecommunication environment between transmitting and receiving terminals.

1. A communication system which has a radio path in a communicationenvironment between a transmitting terminal and a receiving terminal,wherein said receiving terminal calculates a jitter moving average fromthe transmitting and the receiving time of each packet received by saidreceiving terminal and sends the calculated moving average to saidtransmitting terminal; and said transmitting terminal predicts anavailable bandwidth on said radio path based on the jitter movingaverage.
 2. The communication system according to claim 1, wherein thereceiving terminal sends to the transmitting terminal a jitter movingaverage calculated taking positive-valued jitter into account and ajitter moving average calculated taking negative-valued jitter intoaccount as well as a jitter moving average calculated taking onlypositive-valued jitter into account; said transmitting terminal comparesthe both moving averages and predicts the available bandwidth taking theresult of comparison into account.
 3. The communication system accordingto claim 2, wherein when the jitter moving average calculated takingaccount into account not only positive- but also negative-valued jitteris larger than the jitter moving average taking into account only thepositive-valued jitter, the available bandwidth is predicted based onthe jitter moving average calculated taking into account only thepositive-valued jitter.
 4. The communication system according to claim2, wherein when the jitter moving average calculated taking account intoaccount not only positive- but also negative-valued jitter is smallerthan the jitter moving average calculated taking into account only thepositive-valued jitter, the available bandwidth is predicted based onthe jitter moving average calculated taking account into account notonly positive- but also negative-valued jitter, and also the availablebandwidth is predicted based on the jitter moving average calculatedtaking into account only the positive-valued jitter, and an average ofthe results of both predictions is used as a final result of prediction.5. The communication system according to claim 2, wherein the differencebetween the jitter moving average calculated taking only positive-valuedjitter into account and the jitter moving average calculated taking intoaccount not only positive- but also negative-valued jitter; and theresult of the previous prediction is updated in accordance with theratio of the difference to a predetermined threshold value.
 6. Thecommunication system according to claim 1, wherein the amount of packetsto be sent is controlled in accordance with the available bandwidth. 7.The communication system according to claim 1, wherein the packet sendinterval is controlled in accordance with the available bandwidth. 8.The communication system according to claim 1, wherein a packet errorcorrecting scheme is designated in accordance with the availablebandwidth.
 9. The communication system according to claim 1, wherein thetransmitting terminal is connected to a wire path and the receivingterminal is connected to a radio path.
 10. The communication systemaccording to claim 1, wherein the transmitting terminal is connected toa radio path and the receiving terminal is connected to a wire path. 11.The communication system according to claim 1, wherein the transmittingterminal and the receiving terminal are both connected to a radio path.12. The communication system according to claim 1, wherein thetransmitting terminal and the receiving terminal are both connected to awire path; and a mobile terminal is provided on the communicationenvironment to relay packets from the transmitting terminal to thereceiving terminal.
 13. The communication system according to claim 1,wherein the receiving terminal calculates a moving average of areception delay time from each packet reception time and sends thecalculated moving average to the transmitting terminal and, based on themoving average of the reception delay time, the transmitting terminalpredicts the available bandwidth on the radio path.
 14. A transmittingterminal which sends packets to a receiving terminal in a communicationenvironment containing a radio path, wherein upon receiving a jittermoving average from said receiving terminal, said transmitting terminalpredicts an available bandwidth on said radio path based on the jittermoving average.
 15. A receiving terminal which receives packets from atransmitting terminal in a communication environment containing a radiopath, wherein said receiving terminal calculates a jitter moving averagefrom the time of transmission of each packet from the transmittingterminal and the time of reception of the packet and sends thecalculated moving average to the transmitting terminal.